1. Field of the Invention
The present invention relates to an imaging lens. In particular, the present invention relates to an imaging lens for imaging an optical image of an object, an imaging apparatus including the imaging lens, and an information terminal apparatus including the imaging apparatus.
2. Description of the Related Art
Conventionally, an imaging apparatus for imaging an optical image of an object formed on an imaging surface through an imaging lens is known. Generally, the imaging surface of an imaging device included in such an imaging apparatus is flat. Therefore, an imaging lens used in the imaging apparatus is designed so that optical images, in which generation of various aberrations is minimized, are formed on the imaging plane, which is a flat surface (please refer to Japanese Unexamined Patent Publication No. 2006-184783 (Patent Document 1)).
As an imaging device having a flat imaging surface, a CCD (charge coupled device) and a CMOS (complementary metal oxide semiconductor), in which many light receiving pixels are arranged, are known.
Meanwhile, there are a demand for further reduction in the size of the imaging apparatus, which includes the imaging lens and the imaging device as described above, and a demand for higher resolution. Therefore, improvement has been attempted to reduce the thickness of the imaging device while increasing the pixel number of the imaging device. However, when the thickness of the imaging device is reduced, the imaging surface of the imaging device is warped (curved) in some cases. In such a case, the deformation of the imaging surface causes the quality of an image obtained by imaging by the imaging apparatus to deteriorate.
For example, a curvature of field of the imaging lens may be increased so that an optical image formed through the imaging lens follows the shape of the deformed imaging surface that is convex toward the light incident side. However, in some cases, sufficient recovery of the contrast of the optical image formed on the deformed imaging surface is impossible by such a method. Therefore, there is a demand for suppressing a deterioration in the quality of the optical image formed on the deformed imaging surface as described above in a more reliable manner.
Here, the deformation of the imaging surface is convex toward the light incident side of the imaging surface because of production process of the imaging device.